1. Field of the Invention
The present invention relates to a printed-board holding device, an electric-component mounting system and a method of manufacturing a printed circuit board, and more particularly to techniques for holding a printed board.
2. Discussion of Related Art
Many of printed boards have flexibility, since each of them is constituted by a relatively thin circuit board which consists of an electrically insulating material such as a synthetic resin, and a circuit pattern which consists of an electrically conductive material and which is formed on the circuit board. Therefore, where a top surface of the flexible printed board is subjected to an operation for mounting an electric component thereon, an operation for applying a high viscous fluid thereto or other operation, it is not possible to support the printed board with a flatness of the top surface being accurately maintained, unless the printed board is supported at a considerable multiplicity of points of its bottom surface.
Because of that, conventionally, the printed board is supported at its bottom surface by a printed-circuit-board supporting device when the printed board is subjected to an operation. For example, where the printed board has a flat bottom surface without any electric component mounted thereon or without any protrusion portion thereon, the printed-circuit-board supporting device is adapted to include a plate-like supporting member having a large flat supporting surface so that the printed circuit board can be supported at its bottom surface by this plate-like supporting member. For example, a printed-board supporting device described in JP-B2-H2-13475 is equipped with a printed-board supporting stand which is adapted to suck the entirety of the bottom surface of the printed board with application of a vacuum pressure to the bottom surface. The printed-board supporting stand has a multiplicity of sucking holes which open in a supporting surface of the supporting stand, so that the printed board can be sucked with supply of the vacuum pressure to the sucking holes. Since the printed board is sucked by the supporting stand, the printed board is forced onto the supporting surface so as to be flattened by the supporting surface, even if the printed board is convexed in a direction away from the bottom surface toward the top surface. Where the printed board is convexed in a direction away from the top surface toward the bottom surface, the printed board can be flattened by simply bringing the supporting stand into contact with the bottom surface of the printed board and then lifting up the printed board. That is, the downwardly-convexed printed board is flattened without application of the vacuum pressure from the printed-board supporting device, while the upwardly-convexed printed board is flattened by sucking the printed board with application of the vacuum pressure from the printed-board supporting device.
Where the printed board has electric components mounted on its bottom surface, namely, where the printed board has protrusion portions on its bottom surface, the printed board can not be supported at the entirety of the bottom surface. Conventionally, such a printed board having the protrusion portions is supported by a plurality of supporting pins, as in a printed-board supporting device described in JP-A-H11-195899. These supporting pins are brought into contact with respective portions of the bottom surface in which the protrusion portions are not located. In a printed-board supporting device described in JP-B2-3074096 in which a rubber-made suction cup is provided on a distal end portion of each of the supporting pins, the printed board is sucked by the suction cup with application of a vacuum pressure to the bottom surface through the suction cup, while being supported at the bottom surface by a distal end face of each of the supporting pins.